Here is the design of the R6000 antenna made by Cushcraft. It has six bands from 20 meters through 6 meters. This is a simplified model of the most sofisticated R8 antenna.The design takes into the consideration a real soil that following the City Industrial model and the antenna is 6 meters above ground. Antenna shows good characteristics for a vertical with six radio bands and exhibits a typical 1.2:1 SWR in all bands. A 4:1 Balun is used to allow a 50 Ohms input impedance. The surge impedance is 200 Ohms at the antenna feed point, four times higher than the characteristic impedance of the coax. 4NEC2 allows only 0.1 MHz frequency step between 14 and 29 bands. For more details decrease the frequency sweep and the frequency step.